Mucosal cytokines are key components of inflammatory bowel disease (IBD) pathogenesis. This proposal will further define the role of cytokines in IBD by focusing on immunoregulatory molecules originated from two distinct CD4+ T helper cell subsets: Th1 and Th2. Th1-and Th2- cytokines exhibit activities that are likely to be relevant to early disregulation in IBD, as opposed to late tissue-damaging events. To reach our goals we have developed new tissue culture and molecular biology techniques, including isolation and characterization of mucosal T cells from endoscopic biopsies, establishment of T cell lines, clones and hybridomas, Northern blot analysis, PCR, and in situ hybridization. The central hypothesis of this proposal is that a balance between Th1- and Th2-like cells in the gut results in specific cytokine patterns that maintain local immune homeostasis, whereas an imbalance of Th1- vs Th2- like cytokines is present in IBD. This will be tested by four specific aims: 1) Characterization of CD4+ T cells and cytokines in human intestinal mucosa. This will include the isolation of T cells, their phenotypic characterization, the establishment of CD4+ T cell lines, clones and hybridomas, and assessment of their cytokine production; 2) Investigation of Th1- and Th2-like cytokine profiles in normal intestinal mucosa. This will determine which cytokines are produced, if production varies along the gastrointestinal tract, and whether Th1, Th2 or intermediate patterns are present; 3) Investigation of Th1- and Th2-like cytokine profiles in IBD-involved intestinal mucosa. This will determine which cytokines are produced in IBD, whether Th1, Th2 or intermediate patterns predominate, and define the chronic or acute nature of the inflammatory response. 4) Prospective evaluation of Th1- and Th2-like cytokine profiles in IBD. This will provide a dynamic perspective of mucosal cytokines in IBD, improve the detection of specific cytokine patterns, and determine how cytokine profiles vary with clinical status. The identification of mediators responsible for abnormal mucosal immunoregulation in IBD will facilitate searching for inhibitors to control inflammation.